This research project is aimed at the development of analytic methodologies for the construction of severity indexes. It proposes to develop mathematical formulations consistent with clinical judgment to assess severity in relation to predefined purposes which may include need for care, resource consumption, or future outcome. Accordingly, the proposed investigation brings together quantitative analytical skills and selected clinical specialties in a research activity focused on the development of methods that can be used to evaluate the adequacy and appropriateness of medical services and their impact on patient care through the description, and identification of comparable subpopulations. It represents a particular focus of a more general class of research investigations on the development of health status indexes, and as such contributes to that evolving body of knowledge. More specifically it deals with well defined problem entities in relation to the evaluation of the performace of selected components of the health care delivery system. Indexes will be constructed through structured clinician-analyst sessions with appropriate testing. Data from the Florida Trauma Registry will be used to test the indexes. Appraisals will be made of the precision of developed indexes for evaluation or other defined usage as determined by the adequacy, reliability or other inherent weaknesses of data. These estimates will be obtained through phased testing which includes equivalence, iso-severity and multiple value severity testing in applications to specific problem areas in emergency medical services (EMS).